How to restrict the Linux (OS) to limit the number of USB hubs

You probably don't want to do this. For example, if I cut the cable to an existing hub, I can rewire my own one to it in under a couple of minutes.

What are you actually trying to do?

We want to support only three external devices. It is possible to have n number of devices using external USB Hub. I was wondering what I had to do to restrict additional devices if user tried to attach? Do I have to make changes to the Kernal or to make a service to monitor and restrict it? If so then what exactly do I have to do?

Mandar

Why?

Are you doing this for security, ease of programming by only supporting three models of device, ...

Answers kind of depend on why. The kernel may not be the appropriate place for many reasons.